The present invention relates generally to data recording and more particularly to recording heads and other such transducers for recording signals on storage media. Still more particularly, in the most preferred form, the invention relates to recording heads for recording servo-tracking signals on storage media, especially in the form of numerous parallel tracks.
Substantial effort and progress continues toward the goal of increasing the amount of data recorded on a given surface area of record member i.e., storage media. It is essential to the achievement of increased data densities to store each magnetic data signal on the smallest possible surface area of the storage media while retaining the capability of reliably recovering the data stored on the media. This reduction in the surface area necessary to store a magnetic data signal includes placing data-bit signals closer together, which in turn involves increasing the number of data tracks per given surface area of storage media by narrowing the data tracks and placing them closer together.
A significant impediment to accurate recording and recovery of data stored on narrow, closely spaced, tracks on tape media is lateral wander of the record member as it moves longitudinally over the recording head. As data tracks are narrowed and placed closer together, the spacing between the tracks cannot accommodate the lateral wander of the tape media, and consequently a transducer initially aligned to one track may become misaligned as the media is transported past the transducer. Tape wander may take the form of excursions of comparatively large magnitude, both longitudinally to and laterally with respect to the transducer, especially during stopping and starting conditions, but also during steady state longitudinal transport. These large excursions make accurate alignment of the recording head relative to the storage media particularly difficult. Because of the somewhat random occurrence and presence of such conditions, and the nonuniformity of movements of the tape itself, accurate alignment of the recording head relative to the storage media becomes an increasingly important factor as track density increases and the tracks are arranged closer together.
To compensate for lateral tape wander and in an effort to maintain a controlled lateral recording head position relative to the storage media, servo systems have been developed which physically manipulate the recording head position in response to that of the storage media as it is transported past the head. Particularly advantageous servo systems are described in U.S. Pat. No. 4,472,750, issued Sep. 18, 1984 to Klumpp et al., entitled DATA RECORD WITH PRERECORDED TRANSDUCER POSITIONING SIGNALS AND SYSTEM FOR UTILIZING SAME, and U.S. Pat. No. 4,586,094, issued Apr. 29, 1986 to Chambers et al., entitled METHOD AND APPARATUS FOR PRE-RECORDING TRACKING INFORMATION 0N MAGNETIC MEDIA, both of which are assigned to the assignee of the present invention. These sedco systems use servo-tracking centering-signals prerecorded on the storage media as a reference for the recording head, and continuously adjust the position of the recording head to keep it accurately aligned, relative to any selected one of several long tracks of servo signals disposed along the tape.
Although these servo-tracking systems allow significant reduction in the track width and the spacing between tracks on the record member, the ability of manufacturers of magnetic storage systems to make further reductions in the track width, and the spacing between the tracks on the record member, is limited by the ability of transducers to accurately record servo-tracking signals which are narrower and spaced closer together. Known transducers for writing servo-tracking centering-signals on a record member use a write core which sequentially writes the servo-tracking signals for each track by embedding the centering-signals on the storage media one track at a time. Consequently, the servo system is required to accurately, and with high precision, position the recording transducer in each track as the write core records the tracking signal for that track. Due to the excursions of the record member relative to the transducer head, both laterally and longitudinally to the transducer, which occur during stopping and starting as well as steady state transport of the record member, and since recording tape is under tension as it is transported lengthwise, which tension varies subjecting tape media to different amounts of stretching, it is difficult and impractical for a system using a single track write core to accurately align servo-tracking centering-signals longitudinally and laterally as the number of tracks on the storage media increases.
In addition to the difficulties encountered in accurately positioning the single-track transducer for recording the servo-tracking centering-signals due to lateral excursions of the storage media, and longitudinal offsets due to repeated transport of the storage media past the transducer, expended writing centering-signals increases as the number of tracks increase. This increase occurs because the entire length of the record member must be transported past the transducer as the centering signals for each individual track of the storage media are recorded. For storage media having a large number of tracks, the time required to repeatedly transport the storage media past the transducer and record the centering signals becomes excessively large. For example, a forty-track quarter-inch recording tape would require 41 recording passes to record the servo-tracking centering signals by use of such single-track transducer procedures.
Multiple-gap transducers are known which are capable of reading or writing signals from a plurality of different data tracks simultaneously. However, a number of characteristics of these transducers prevent them from being truly effective or desirable for recording multiple-track servo-tracking signals for high density data storage. For example, stacked-core transducers include multiple cores isolated magnetically from each other and having respective gaps which are spaced apart by a distance at least equal to one track width. These transducers are relatively complex in construction and thus are costly to manufacture due to the number of cores and windings which make up the transducer. Additionally, it is necessary to balance the different transducer cores to compensate for variations in the flux generated by respective ones of the cores, in an effort to produce generally uniform signals from all the cores. Further, the physical dimensions of each of the cores which form the respective gaps of such stacked-core transducers limit the number of cores which can be stacked for a particular width of tape due to the thickness of the core material required to give the legs of the core structural strength and a geometry for generating flux in the storage media. The width of the respective cores added to the thickness of the magnetic insulator between each core essentially prevents the use of stacked-core transducers to record adjacent, closely spaced, tracks.